FIG. 1 illustrates a radio system 10 comprising a plurality of radio receiver terminals 12A, 12B, 12C, 12D and a plurality of broadcasting antennas 14A and 12B. In this example, each terminal is tuned to a broadcast radio channel 16A, 16B corresponding to a particular commercial radio station such as Jazz FM, for example. The frequency of the broadcast radio channel used for this radio station by the antennas 12A and 12B may differ, but the content of the information transmitted is the same.
Each terminal 12 converts at least some of the information received via the broadcast radio channel into audible sound. The user of a terminal is therefore able to listen to the audio content provided by the radio station to which the radio terminal is tuned.
The broadcast radio channel may also be used to communicate additional information by embedding it within the broadcast information. The additional information may be used to provide specified services such as traffic announcement TA and traffic programme TP or may be used to provide unspecified services such as open data applications (ODA).
According to the Radio Data Services (RDS) specification, the type 3A group conveys information about which Open Data Applications (ODA) are carried on a particular transmission and in which groups they will be found. The group 3A consists of two elements the Applications Identification (AID) code and the Application Group Type code used by the application. The Application Group Type code indicates the group type used, in the particular transmission, to carry the specified ODA information. The AID identifies which application the terminal needs to use. The identified application then uses the ODA information to provide a service at the terminal.
The inventor has realized that a problem may arise, if a malicious broadcaster masquerades as the radio station and provides unauthorized ODA information.
It would be desirable to enable a terminal to authenticate the received ODA information, but this is not straightforward in a broadcast or uni-directional radio channel.